Few things could be up with that.
1st. check to make sure your radiator is full, also check to see how strong your antifreeze is with a little ball gauge. If you don't have the mix right ( too much antifreeze and not enough water) it will take longer to heat up.
2nd, if all that is good than it could be you need to replace the thermostat with a new one.
3rd. worst case could be a clogged heater core which might need to be flushed to clean out any debris that might be clogging the water ways. Hope this helps.
Low coolant? Bad thermostat? Heater core restricted, plugged or airbound? Temperature control not working? Water pump not circulating coolant?
you can blow fuses or the battery Possible computer damage.
The blower on the back heater may need to be replaced on the 2000 Ford Winstar.
you may not have the heater water hoses plugged in
you would have to see a mechanic about that problem
probably the heater core is clogged
Coolant level is most likely low and going up hill allows it to reach the heater core.
Check for low coolant
Mercury did not blow up.
Faulty thermostat. Plugged heater core. Temp blend door malfunction.
heater will not blow on a 1996 ford contour
if the heater does not blow out warm air change the setting.